As an image processing technique of properly reproducing the same color image in a plurality of image input/output apparatuses, a CMS (Color Management System) is known.
A CMS will be described by exemplifying the case where a plurality of apparatuses such as a color printer, color monitor, and color copying machine are connected to each other, as shown in FIG. 31.
According to the CMS, a color signal in an input system is transformed into a color signal in an output system. More specifically, an input color signal is transformed into a signal in a color space independent of an apparatus (to be referred to as a device-independent color space hereinafter) by using a predetermined transformation formula or table associated with an input apparatus. The predetermined transformation formula or table used to transform a signal in a color space dependent on an apparatus into a signal in a device-independent color space will be referred to as a profile for the apparatus.
After a signal value to be output is obtained by performing predetermined color processing for the transformed signal in the device-independent color space, the signal value is transformed into a signal in a color space dependent on each output apparatus by referring to a profile for each output apparatus.
As described above, according to the CMS, color matching between a plurality of apparatuses can be realized by transforming a color signal in a color space dependent on each apparatus into a color signal in a device-independent color space on the basis of the profile for each apparatus.
In general, as a device-independent color space, the CIE/XYZ color space, CIE/L*a*b* color space, or the like which is a color space used for colorimetry of an image output from an output apparatus is used.
A profile for each apparatus is created on the basis of the relationship between each color signal value and the value obtained by actual colorimetry of a visible image input to the apparatus or output therefrom. For example, a profile for an input apparatus is created by using a sample image as an original which is based on a predetermined color signal on the basis of an input image signal obtained through the apparatus. A profile for an output apparatus is created by outputting a sample image based on a predetermined color signal in the apparatus and calorimetrically measuring the output sample image.
However, the color reproduction characteristic of an image input/output apparatus does not necessarily remain the same at the time of creating of a profile and at the time of execution of a CMS using the profile. This phenomenon occurs when the color reproduction characteristic of an image output apparatus varies more or less due to differences between parts such as color material lots in the apparatuses, environmental differences such as temperature/humidity differences, changes in the quality of image forming components and the like over time, or the like. When the color reproduction characteristic changes after the creation of a profile, the relationship between each color signal and the corresponding calorimetric value of an output image, which is reflected in the profile, changes. Obviously, therefore, when the CMS is executed without any change, a proper color reproduction result cannot be obtained.
If, therefore, the color reproduction characteristic of an image input/output apparatus greatly changes, the profile must be updated. The conventional CMS, however, provides no means for allowing a user or person who maintains a profile (to be referred to as a profile manager hereinafter) to check a change in the color reproduction characteristic of an image input/output apparatus and determine the validity of the profile. For this reason, profile update processing is not always performed at a proper timing.